With his cameo in Knight of Cups, Peter Matthiessen qualifies.
Among other things, he was the only winner of National Book Awards for fiction and nonfiction.

From his New York Times obit:

"Mr. Matthiessen was a man of many parts: littérateur, journalist, environmentalist, explorer, Zen Buddhist, professional fisherman and, in the early 1950s, undercover agent for the Central Intelligence Agency in Paris. Only years later did Mr. Plimpton discover, to his anger and dismay, that Mr. Matthiessen had helped found The [Paris] Review as a cover for his spying on Americans in France."